Just bought my second Wrangler ('07 JK 4DR) a month ago. Got it with a 4"inch lift already on to save some labor money. As a result I don't know what the manufacturer is or what all the kit included since I'm not real knowledgeable about lifts.

I put a 2 inch on my old TJ and noticed a reduction in stability on the highway (as expected). But the 4 inch on the 4 door has caused random fits of instability above 50mph. I wanted to know if there is a way to create more stability at speed. I don't think it's what people are describing as the death wobble-more of lateral movement at speed. I know you can't change the dirty air or bad aerodynamics so please don't say "get another vehicle", "take off the lift" or something similar. I know there is a ton you can do to improve suspension performance with many cars so I was wondering if anybody has found an effective upgrade for lifted jeeps.

How is caster corrected by your suspension? Adjustable upper or lower front control arms? AEV or some other brackets? Not at all?

Have you been to an alignment shop to get your alignment numbers? Flighty steering is a symptom of insufficient caster angle.

Also, are your axles centered on the Jeep? Do you have adjustable trackbars or relocation brackets either frame or axle side to center the axles? You can check for centered axles by looking at the tire/fender relationship on each side at each axle. If the tires stick out further on one side while the Jeep is at rest the axles aren't centered. (Unlikely, but it could be that an adjustable track bar has been set too lng too.)

My bet is that its an incomplete lift that doesn't properly resolve caster angle issues and/or doesn't center the axles.

Check out the Jeep and answer the questions and you will be providing answers to Q's that are needed to help further diagnose your issues.

On my rig, lifting reduced the caster angle to the point the thing flitted all over the road. I had the adujstable cam bolts instaleld and teh caster angle brought back to fiveish degrees, and it much, much more stable now.

I'm told this makes low speed steering more difficult, but with power steering, I just really don't care.

As a previous post said, you probably need adjustable control arms. Anytime you add a lift, it throws off the suspension geometry, which could cause the exact problem you are describing.
I would start with purchasing the adjustable lower control arms,and go from there.

Just bought my second Wrangler ('07 JK 4DR) a month ago. Got it with a 4"inch lift already on to save some labor money. As a result I don't know what the manufacturer is or what all the kit included since I'm not real knowledgeable about lifts.

I put a 2 inch on my old TJ and noticed a reduction in stability on the highway (as expected). But the 4 inch on the 4 door has caused random fits of instability above 50mph. I wanted to know if there is a way to create more stability at speed. I don't think it's what people are describing as the death wobble-more of lateral movement at speed. I know you can't change the dirty air or bad aerodynamics so please don't say "get another vehicle", "take off the lift" or something similar. I know there is a ton you can do to improve suspension performance with many cars so I was wondering if anybody has found an effective upgrade for lifted jeeps.

Thanks guys.

Yes, adjustable front control arms to fix your castor is the answer. Also reduce the air pressure in your tires.
I bought my '07 with a 4 inch lift in Georgia and it was so scary on the highway, I took back roads all the way back to Nashville.
I aired down my 35's to 26 psi and that helped some. I then put adjustable uppers and that helped immensely. I just got done putting on adjustable lowers and it is even better.
If I had to do it over again, I would probably get fixed lowers that are about 1/2 inch longer than stock, then the adjustable uppers. That would have accomplished the same thing but would have saved me some bucks.

Before committing to adjustable control arms, which are pricy, take a look at AEV's front control arm brackets, which run $100 the pair and which will probably save your front drive shaft, as well as reduce break dive and body roll.

I believe that I've got 5-to-6-degree caster on my stock front axle with my 3" TeraFlex lift (TeraFlex designates length measurements for upper/lower control arms, thus automatically setting caster). With wheel centered and proper toe-in she drives perfect up to 80mph (130km/h - I rarely drive that speed and I don't drive faster that that). I have the full-flexarm lift kit and she drives like a dream, pretty sure that the adjustable control arms is key.